Electrical heating element



Jan. l, 1946.. l J, MCORLLY 2,391,995

ELECTRICAL HEATING ELEMENT Filed Aug. 6, 1945 HIJ/11141 wal/1.1141

, ci el tis by 'suitably y 'f the re- 33 wi e the sheath. 2l. and then adding 'cm'meterial to embed the tor, and.'

terebly compel-:ting the embedding material; in any suitable rnenner.

The cest plete type o heating element shown A in es 7 and B, comprises n sheath cog o? n cest metall plete 33 provided with grooving 3d in which is disposed e resistor ist embedded in embedding mcte'riel Se end connected to termi= nele 8i? projecting beyond the embedding meterlel dii. @ne wey ci m this type oi element is by genernlly the seme process 'described for the tsm elements shown in Figures l. through- 3, ci course omitting the steps of adding the cover plete end turning over the mnrgins of the channel. l

in electric heating elements ci the types herein. shown end shove described, and likewise in embedded-resistor electric Vhee-ting elements of verious other es, previously it hes been customer-y to employ es the embedding material e composion comprising essentially granular reflector?,7 materiel, lor esempio, Zircon, el, sillimenite, or e eend bcnmeteriel, for ple, cles or lseolln, and suoli compositions have beensfcceptsbie, end still ore acceptable, under low perioce. Y

However, by wey of ple, ring type elements es shown in l through s, and else cest blote type elements es shown in Figures 'l 'and d, ere ci e, form inherently highly suitable lor elec- Vme hot piste units end electric ronge top imite.

Qn the other hond, for such-units to be satisfectory los tnet purpose, the embedding material must bev-high heet conductim, low electrical leek cele, and suitable for operation, et red heeft or According to my invention, this may be escom'a piished by elimlneting the previous bonding rneterici, end including e, quantity of telo. Further, vcontraire; to what might be. expected, the telo not only provides the desirable worlzebllity of the com Yposition in endearing the mening of the element, but 'apparently serves else to mit the granuler mettermi et leestsumciently to hold the resistor 'ond the tels in position, end on the other hond, within limits, does not obj ectionsbly reduce the thermal conductivity, et lee-st in terms of ebilitlfv of the' embedding to conduct the heet from the resister. 4

Oi cernes the elietion oi the previous bonding mnterlei, end to some extent the inclusion o thetelo, result in very greet enhancement of the elecnics velues, including very large decrease in the electrical lenkt-isnV However, et leest on the besis ci what I have thun ier been sible to eccomplishfto produce-sn embedding eepnble of holding the resistor and the terminals in position, the talc must be present in en cmi notices than approximately 8%,

l sind to avoid obiectionnble decrease in the ability Y 'o2 the embedding to conducttheheet from the r the talc must not be included in an ernennt more i. f approximately 4.0%, end preislnould not be includedfin amount more telybvweisht. Y

Onthe other hand; et leest accor to present indicscne, with the inclusion of talc, seemingly there ins-nc disadvantage, end 4epperently'se sdcantsge, at leest in somefinstences, in includ- Yingfelsee quantity o2 the previous bonding md- For exemple, the inclusion oi e quantity oi the previous embedding materiel generally will :esuli-. "i

' l dnd the reason of dispersion of the previous bonding me terial by the talc, will not obiectionably increase the electrical leakage, or obiectionably impen-A ony oi the other electrical values.

' However, at least onsthe basis of what I have thus fer been able to accomplish, the previous bonding materiel, il it is included, should not be present in en amount more than epproximstelv 29%, end'preferebly should not be present in en amount more then approximately 15%,Y by weight.

By was' of exemple, en excellent embedding material results from e. composition consisting oi approximately '78% granular material, 17% i'nlc,A

and 7% bonding materiel, by weight, the granular materiel being Zircon, and the bondingI materiel being kaolin.

This composicion, in t. suitably moist condition, may be introduced into the sheath, Vand the resisf ,tori embedded thereimond the composition compacted, as above described, end when'dried' and baked produces e, ilrm celere, oi low electrical Heating elements employing this embed may be operated safely, for exemple, creed in liquid, et wett densities ci 50 to 60 wette per square inch oiheeting suri'dce. 'The thicmess' of the embedding materiel between the posses ci the resistor, and between the resistor and the sheath; muy be smell, for exemple, es' little es epprommetely 0.07 to 0.09 oi7 en inch. with 'the' element operated et temperatures oi thev order oi i260" to 1600 lFshrehlieit, the electrical ieeknge nevertheless is very smell, and only e, frection of the electrical leekage in a similar elementV the previousivembedding materiel end 'operated et only 30 to 40 watts per square inch empio' end therefore et materielle lower temperature.

Therefore en embedding oi the above composition is particularly suitable for electric hot plete units and electric ronge top units, intended for operation et high ffthe embedding can expend, contract, and bend, A

without showing creeks.

Therefore this composition le particularly edventegeous in instances involving ieletively long length of embedding end eggravated problems oi contraction end expansion, for. exemple. in cest plete type heating elements as shown in Figures 7 and 8.

Other particular compositions are, including rbon materiel. apprommately '76% grenular terial, 6% telo, end 18% bonding materiel, and

eppetely 69% granular materiel, 35% telo.' and 5% bonding materiel, end not including bond= ing materiel, apprommetely A% granules meterisl and 5% telo, approximately 80% grenuler materiel end 20% talc, end cpproximotelil7 6% grsnularmcterial end 35% telo, by weight, end

peinture,v and nevertheless Y limited to very low electricsl leakage. l

Apparently themesh.

Forthe bonding materiaL-in most instances I prefer kaolin, but I may use ball clay, or semi-ball ment comprising embedding having high heat conductivity and iow'electrical leakage and suitable for operation at red heat, consisting of clay, either alone or .in conjunction with kaolin. 1

However, apparently it is preferable that the alkali content of the kaolin or clay be not more than ap- `proximately 0.25%, that the calcium oxide content also should be low, that no chemical be used in washing the -iraolin or clay, either basic or acid, te avoid absorption, and that the lraolin or clay be dried and pulverized to a substantially uniform ilneness of air-iioat size.

For the talc,apparently it is desirable to use an electrical grade of talc, and apparently it is preferable that the talc be low in lime and alkali salts or other impurities, and white-burning. in this connection it is 'to be understood vthat the term talcis herein used generically, and under proper circumstances includesvlor example soapstone and steatite.

In pressing the composition i may use pressures as low as 500 pounds or less, up to 10 to 15 tons or more, per square inch, depending on the circumstances in the particular instance, and likewise drying may beat room temperature, or above or below, and baking may be at a temperature, ior example, of the order of 1200 `lahrenheit, or higher or lower.

Further, as will be understood bythose skilledv in the art, the :tour types oi heating units shown in the drawing are illustrative only, and also, while reference has been madeto embedding `ruaterial having high heat conductivity'and low electrical leakage and suitable'for operation at red heat, of course this merely is definitive of the embedding, and the temperature at which the element or embedding actually-is operated, is iin-` material. v y

Accordingly, it will be obvious to those skilled in the art, that I have accomplished at least the principal object of my invention, and on the otherhand, that the disclosure herein is illustrative only, and that my invention is not limited thereto.

Now, therefore, I claim as follows: i

1. |An embedded-resistor electric heating element comprising embedding having high heat conductivity and low' electrical leakage and suitable for operation at red heat, consisting of material compacted under pressure. comprising .granular refractory material 1-oit high heat conductivity and low electrical leakage, and comprising also talc, the talc constituting approximately 3% to approximately 40%, and the granular material and talc constituting at least approximately 80%, by weight. i

2. An embedded-.resistor electric heating element comprising embedding having high heat conductivity and low electrical leakage and suit. able for operation atred heat, consisting .of material compacted under pressure, and comprising talc approximately 3% to approximately 40%, by weight,and the remainder-substantially entirely material compacted under pressure, comprising granular refractory material of high heat conductivity and low electrical leakage, and comprising also bonding material and talc, the talc constituting approximately 3% to approximately the bonding material constituting not more than approximately 20%, and the' granular material and talc constituting at least approximately by weight.

4. An embedded-resistor electric heating element comprising embedding having high heat conductivity and low electrical leakage and suitable for operation at red heat, consisting of material compacted under pressure, comprising granular refractory material of high heat con- -ductivity and low electrical leakage, and comprising also talc, the talc constituting approximately -3% to approximately 30%, and the 2Tanular material and talc constituting at least approximately 85%, by weight.

5. An embedded-resistor electric heating ele-k ment comprising embeddinghaving high heat conductivity and low electrical leakage and suitable for operation at red heat, consisting or vmaterial compacted under pressure, and comprising talc approximately 3% to approximately 30%, by weight, and the remainder substantially entirely granular refractin'y` material of high heat conductivity and low electrical leakage.

6. An embedded-resistor electric heating ele ment comprising embedding having high heat conductivity and low electrical leakage and sultable for operation at red heat, consisting oi material compacted under pressure, comprising granular refractory material oi high heat conductivity and low electrical leakage, and comprising also bonding material and talc, the talc constituting approximately 3% to approximately' 30%, the bonding material constituting not more than approximately 15%, and the granular material and talc constituting at least approximately 85%, by weight.

'7. An embedded-resistor electric heating element comprising embedding having high heat conductivity and low electrical leakage and suitable Ior operation at red heat, consisting ot material compacted under pressure, and compricing granular refractory material of high heat conductivity and low electrical leakage, approximately '15%, and talc, approximately 7%, and

' able for operation at red heat, consisting of granular refractory material of high heat conductivity and'low electrical leakage. 4

a. sn embedded-muestra mung exe- 5 material compacted under. pressure, and ,com-

prising granular refractory material of high heat conductivity and low electrical leakage. approximately '78%,' and talc, approximately 17%, and l bonding material, approximately 7%.

9. An embedded-resistor electric heating `elc-v ment comprising embedding having high host conductivity and low electrical leakage and suitable for operation at red heat, consisting of material compacted under pressure, and comprising granular refractory material oi high heat conductivity and low electrical leakssaapproximately 60%, and talc. approximately 35%. and` I bonding material, approximately 5%.

JOSEPH HoORLLY. 

